CN113792414B - Method for predicting fatigue life of ceramic matrix composite under variable amplitude loading - Google Patents
Method for predicting fatigue life of ceramic matrix composite under variable amplitude loading Download PDFInfo
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- CN113792414B CN113792414B CN202110958637.1A CN202110958637A CN113792414B CN 113792414 B CN113792414 B CN 113792414B CN 202110958637 A CN202110958637 A CN 202110958637A CN 113792414 B CN113792414 B CN 113792414B
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- 239000011153 ceramic matrix composite Substances 0.000 title claims abstract description 24
- 238000000034 method Methods 0.000 title claims abstract description 22
- 230000015556 catabolic process Effects 0.000 claims abstract description 23
- 238000006731 degradation reaction Methods 0.000 claims abstract description 23
- 238000001228 spectrum Methods 0.000 claims abstract description 16
- 238000009661 fatigue test Methods 0.000 claims abstract description 7
- 239000000463 material Substances 0.000 claims abstract description 7
- 238000012545 processing Methods 0.000 claims abstract description 5
- 238000009825 accumulation Methods 0.000 claims abstract description 4
- 239000002131 composite material Substances 0.000 claims description 7
- 238000012360 testing method Methods 0.000 abstract description 3
- 238000002474 experimental method Methods 0.000 abstract 1
- 238000011160 research Methods 0.000 description 6
- 238000013461 design Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000000956 alloy Substances 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/20—Design optimisation, verification or simulation
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- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2113/00—Details relating to the application field
- G06F2113/26—Composites
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
- G06F2119/04—Ageing analysis or optimisation against ageing
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
- G06F2119/14—Force analysis or force optimisation, e.g. static or dynamic forces
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract
The invention discloses a method for predicting fatigue life of a ceramic matrix composite under variable amplitude loading, which comprises the following steps: step 1, carrying out a fatigue experiment of a ceramic matrix composite material, and establishing an equal-life curve; step 2, fitting a stiffness degradation model, and determining parameters in the model; step 3, processing an amplitude-variable load spectrum; and 4, calculating damage accumulation and service life based on rigidity degradation. The service life prediction under amplitude variation is performed based on the rigidity degradation of the ceramic matrix composite, and the required data can be obtained in the basic fatigue test process, so that the test cost is saved.
Description
Technical Field
The invention relates to a method for predicting fatigue life of a ceramic matrix composite under variable amplitude loading, and belongs to the field of fatigue performance of ceramic matrix composites.
Background
The ceramic matrix composite material not only has the advantages of high modulus, low density and good thermal stability, but also has better high-temperature performance and strength compared with the traditional high-temperature alloy, and has been widely applied to the fields of aerospace, military and the like. The structural member of the ceramic matrix composite is subjected to stretching, compression and alternating stress in an actual working environment, so that the service life of the structural member is far lower than the design life of the structural member, economic loss is caused, and even serious accidents occur. Therefore, the research on the fatigue performance of the ceramic matrix composite is of great importance, and plays a key role in optimizing the design of the composite.
At present, the research on ceramic matrix composite materials is mainly focused on performance research under static load and fatigue constant amplitude load, and the fatigue performance research under variable amplitude load is mainly related to a life prediction method under load block loading (high-low load or low-high load), but the fatigue performance research on load amplitude change is still less. Therefore, the method for predicting the service life of the ceramic matrix composite under reasonable and effective amplitude variation is particularly important.
Disclosure of Invention
The invention aims to provide a method for predicting the fatigue life of a ceramic matrix composite under variable amplitude loading, which is characterized in that variable amplitude load is regarded as the combined action of a plurality of loads, and the difference of stiffness degradation trends under different load levels is utilized to accumulate the stiffness degradation under each stage of load so as to calculate the fatigue damage of the composite. The method can predict the fatigue life of the composite material by using less test cost, and provides technical support for the research of the ceramic matrix composite material under variable amplitude load.
In order to achieve the above purpose, the invention adopts the following technical scheme:
step 1, performing a fatigue test of a ceramic matrix composite material, and establishing an equal-life curve;
and carrying out fatigue tests of the ceramic matrix composite under stress ratios R=0.1 and R= -1 to obtain S-N curves with two stress ratios, drawing an equal life curve of the composite according to the S-N curves with the two stress ratios, obtaining corresponding fatigue life according to different stress and stress ratios by utilizing the equal life curve, substituting the life data into a corresponding rigidity degradation model, and carrying out subsequent calculation.
Step 2, fitting a stiffness degradation model, and determining parameters in the model;
v 1 ＝p 1 σ max +p 2 v 2 ＝p 3 σ max +p 4
wherein E is 0 Is the initial stiffness; e (n) is the residual stiffness; sigma (sigma) max Is the maximum value of the applied stress; n is the cycle number of the current load; n is the lifetime of the current load level; a and b are fitting parameters, and are irrelevant to stress; q, v 1 、v 2 All stresses establish a relationship, wherein c1, c2, p1, p2, p3, p4 are fitting parameters.
Step 3, processing an amplitude-variable load spectrum;
and removing load points which are neither peak points nor valley points in the amplitude-variable load spectrum, so that the processed load spectrum only comprises the peak points and the valley points. Carrying out rain flow counting treatment on the treated load spectrum to obtain stress amplitude sigma under each cycle a Average stress sigma m And maximum stress sigma max Sigma is calculated as a 、σ m Sum sigma max Substituting the model into an equal life curve and a stiffness degradation model respectively for calculation.
Step 4, calculating damage accumulation and service life based on rigidity degradation;
the damage caused under the first stage load is:
D 1 ＝E 0 -E(n 1 )/E 0 -E f1
wherein E is 1 Is the residual rigidity after the first stage load is acted; e (E) f1 Is the critical stiffness for first stage load failure.
Under the second-stage load, the equivalent number of cycles required to produce the same damage is n 21 ，
D 21 ＝E 0 -E(n 21 )/E 0 -E f2
According to D 1 ＝D 21 Can obtain the equivalent cycle number n 21 Thus, the residual stiffness E (n) 1 +n 2 ) The method comprises the following steps:
and the rest rigidity after the m-level load is acted can be obtained by the same method, so that the total damage after the m-level load is acted is obtained:
the fatigue life is the reciprocal of the total damage:
N＝1/D m
the fatigue life prediction method for the ceramic matrix composite under variable amplitude loading has the following advantages:
1. the stiffness degradation model provided by the invention can be fitted with three stages of stiffness degradation trends under different loads, so that the life prediction has higher accuracy.
2. The method provided by the invention is based on the mode of rigidity degradation to accumulate damage, and the stress strain data required by the rigidity degradation can be completely obtained in the S-N curve making process, so that the test cost is saved.
Drawings
FIG. 1 is a flowchart of a fatigue life prediction procedure;
FIG. 2 is a schematic illustration of an equal life curve;
FIG. 3 is a luffing load spectrum;
FIG. 4 is a processed load spectrum;
fig. 5 is a schematic diagram of stiffness degradation under luffing loads.
Detailed Description
Description of specific embodiments of the invention with reference to the drawings
As shown in FIG. 1, the method for predicting the fatigue life of the ceramic matrix composite under variable amplitude loading provided by the invention comprises the following steps:
step 1, performing a fatigue test of a ceramic matrix composite material, and establishing an equal-life curve;
and carrying out fatigue tests of the ceramic matrix composite under stress ratios R=0.1 and R= -1 to obtain S-N curves with two stress ratios, drawing an equal life curve of the composite according to the S-N curves with the two stress ratios and according to the method shown in fig. 2, obtaining corresponding fatigue life for different stress and stress ratios by utilizing the equal life curve, substituting the life data into a corresponding rigidity degradation model, and carrying out subsequent calculation.
Step 2, fitting a stiffness degradation model, and determining parameters in the model;
v 1 ＝p 1 σ max +p 2 v 2 ＝p 3 σ max +p 4
wherein E is 0 Is the initial stiffness; e (n) is the residual stiffness; sigma (sigma) max Is the maximum value of the applied stress; n is the cycle number of the current load; n is the current load levelThe service life; a and b are fitting parameters, and are irrelevant to stress; q, v 1 、v 2 All stresses establish a relationship, wherein c1, c2, p1, p2, p3, p4 are fitting parameters.
Step 3, processing an amplitude-variable load spectrum;
as shown in fig. 3, an arbitrary amplitude load spectrum is shown, and load points which are neither peak points nor valley points in the amplitude load spectrum are removed, so that the processed load spectrum only contains the peak points and the valley points, as shown in fig. 4. Carrying out rain flow counting treatment on the treated load spectrum to obtain stress amplitude sigma under each cycle a Average stress sigma m And maximum stress sigma max Sigma is calculated as a 、σ m Sum sigma max Substituting the model into an equal life curve and a stiffness degradation model respectively for calculation.
Step 4, calculating damage accumulation and service life based on rigidity degradation;
as shown in FIG. 5, which shows a schematic diagram of the stiffness degradation of a two-stage load, it is assumed that cycle n is under a first stage load 1 Second, cycle n under second stage load 2 The damage caused under the first stage load is then:
D 1 ＝E 0 -E(n 1 )/E 0 -E f1
wherein E is 1 Is the residual rigidity after the first stage load is acted; e (E) f1 Is the critical stiffness for first stage load failure.
Under the second-stage load, the equivalent number of cycles required to produce the same damage is n 21 ，
D 21 ＝E 0 -E(n 21 )/E 0 -E f2
According to D 1 ＝D 21 Can obtain the equivalent cycle number n 21 Thus, the residual stiffness E (n) 1 +n 2 ) The method comprises the following steps:
and the rest rigidity after the m-level load is acted can be obtained by the same method, so that the total damage after the m-level load is acted is obtained:
the fatigue life is the reciprocal of the total damage:
N＝1/D m 。
Claims (2)
1. a method for predicting fatigue life of a ceramic matrix composite under variable amplitude loading is characterized by comprising the following steps of:
step 1, performing a fatigue test of a ceramic matrix composite material, and establishing an equal-life curve;
developing fatigue tests of the ceramic matrix composite under stress ratios R=0.1 and R= -1, so as to obtain S-N curves with two stress ratios, and drawing an equal-life curve of the composite according to the S-N curves with the two stress ratios;
step 2, fitting a stiffness degradation model, and determining parameters in the model;
v 1 ＝p 1 σ max +p 2 v 2 ＝p 3 σ max +p 4
wherein E is 0 Is the initial stiffness; e (n) is the residual stiffness; sigma (sigma) max Is the maximum value of the applied stress; n is the cycle number of the current load; n is the lifetime of the current load level; a and b are fitting parameters, and are irrelevant to stress; q, v 1 、v 2 Establishing a relationship between the average stress and the stress, wherein c1, c2, p1, p2, p3 and p4 are fitting parameters;
step 3, processing an amplitude-variable load spectrum;
removing load points which are neither peak points nor valley points in the amplitude-variable load spectrum, so that the processed load spectrum only contains the peak points and the valley points, and carrying out rain flow counting processing on the processed load spectrum;
step 4, based on damage accumulation under rigidity degradation;
calculating the residual rigidity after the m-level load is acted, thereby calculating the total damage D after the m-level load is acted m ：
i is the serial number of the multi-stage load; the fatigue life N is the total damage D m Is the reciprocal of (2):
N＝1/D m 。
2. the method for predicting fatigue life of ceramic matrix composite under luffing loading of claim 1, wherein: the stiffness degradation model established by the method fits three stages of stiffness degradation of the composite material, and the problem of amplitude loading is solved by establishing a relation with stress.
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Citations (4)
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|---|---|---|---|---|
| WO2013105995A2 (en) * | 2011-02-25 | 2013-07-18 | Board Of Supervisors Of Louisiana State University And Agricultural And Mechanical College | Fatigue monitoring for composite materials |
| CN108693054A (en) * | 2018-05-18 | 2018-10-23 | 北京航空航天大学 | A kind of composite structure spectrum carries the progressive damage algorithm of fatigue life |
| CN111368473A (en) * | 2020-03-04 | 2020-07-03 | 北京航空航天大学 | CFRP-metal hybrid bolt connection structure fatigue life prediction method under competitive failure |
| CN112051146A (en) * | 2020-08-31 | 2020-12-08 | 沈阳建筑大学 | Fatigue life prediction method for fiber metal laminate under complex load |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2803968B1 (en) * | 2013-05-13 | 2019-05-08 | Siemens Industry Software NV | A process for calculating fatigue and fatigue failure of structures |
| US9274036B2 (en) * | 2013-12-13 | 2016-03-01 | King Fahd University Of Petroleum And Minerals | Method and apparatus for characterizing composite materials using an artificial neural network |
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- 2021-08-20 CN CN202110958637.1A patent/CN113792414B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013105995A2 (en) * | 2011-02-25 | 2013-07-18 | Board Of Supervisors Of Louisiana State University And Agricultural And Mechanical College | Fatigue monitoring for composite materials |
| CN108693054A (en) * | 2018-05-18 | 2018-10-23 | 北京航空航天大学 | A kind of composite structure spectrum carries the progressive damage algorithm of fatigue life |
| CN111368473A (en) * | 2020-03-04 | 2020-07-03 | 北京航空航天大学 | CFRP-metal hybrid bolt connection structure fatigue life prediction method under competitive failure |
| CN112051146A (en) * | 2020-08-31 | 2020-12-08 | 沈阳建筑大学 | Fatigue life prediction method for fiber metal laminate under complex load |
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